1. Field of the Invention
This invention relates to check valves. More particularly, this invention relates to check valves having a pre-set cracking pressure.
2. Description of the Background Art
Presently, there exist many types of check valves designed to control the one-way flow of a fluid therethrough. More particularly, one predominant type of check valve comprises a ball reciprocatingly positioned within a caged area of a fluid passageway. The flow of fluid in one direction through the passageway is uninhibited (unchecked) as it flows around the ball to exit the passageway. However, in the opposite direction, the flow of fluid forces the ball against a valve seat, thereby inhibiting (checking) the flow of fluid therethrough. Many variations of this basic embodiment of a check valve have been developed over the past many decades that check valves have been in use, each having certain advantages when used in certain applications.
In one application area, check valves, commonly referred to as "catheter" check valves, have been developed to control the one-way flow of a fluid into an inflatable bulb of a catheter or endotracheal tube or in similar relatively low-pressure applications. Indeed, due to the relatively low back pressure exerted on the valve element to urge it against the valve seat, it is usually desirable to provide means for constantly urging the valve element against the valve seat such that the valve remains closed when little or no back pressure is present. Consequently, check valves of this nature have a pre-set cracking pressure which must be exerted on the valve element to unseat itself from the valve seat allowing the flow of the fluid in the unchecked direction,
For example, U.S. Pat. No. 3,831,629, the disclosure of which is hereby incorporated by reference herein, discloses a check valve comprising a valve element which is constantly urged in sealing engagement with a valve seat thereby maintaining the valve in a closed condition even during the complete absence of back pressure exerted on the valve. Moreover, a certain amount of forward cracking pressure must be exerted on the valve element in the unchecked direction to unseat the valve element, allowing the flow of fluid therethrough. As illustrated and discussed in said patent, such positive cracking pressure may be overcome by means of a mechanical instrument, such as a syringe, by fluid pressure, or by combination of the same.
After more than a decade of experience with the check valve disclosed in said patent, the Assignee of said patent and of this application, has realized that there are some disadvantages associated with the check valve manufactured in accordance with that patent. First, while the valve element may be mass-produced for use in a large variety of valves, differently dimensioned valve bodies or valve elements must be produced in order to provide a variety of valves having different cracking pressures. Consequently, a significant inventory of injection molds and related equipment must be continually developed depending upon the needs of each particular customer. Thus, the ability to provide check valves of this nature with different degrees of cracking pressures necessarily results in an increase in the cost of manufacture because of the inability to produce a universal body usable in conjunction with a universal valve element to produce different valves having different cracking pressures.
In view of the foregoing, there existed a need for a check valve which permitted a universal-size valve element to be positioned into a universal-sized valve body in such a manner that the check valve could be assembled with different cracking pressures. As set forth in U.S. Pat. No. 4,681,132, the disclosure of which is hereby incorporated by reference herein, this need was satisfied by the discovery of a specially configured apertured plug positioned in the output passageway of the check valve. During production, plugs of a different size could be positioned in the output passageway so as to increase or decrease the distance between the plug and the valve seat of the valve housing, thereby decreasing or increasing, respectively, the amount of cracking pressure necessary to open the valve. The check valve employing differently-sized plugs as set forth in U.S. Pat. No. 4,681,132 has enjoyed wide commercial success because of the ability to more precisely set the cracking pressure of the valve.
The above-referenced patents owned by this Assignee further disclose various embodiments of the valve element itself. For example, as shown in FIGS. 5-8 of U.S. 3,831,629, it is seen that the valve element may comprise a substantially cylindrical-wall configuration (FIG. 5), a three point star-configuration (FIGS. 6 and 7), or a bellows configuration (FIG. 8). A similar star-configuration of a valve element is illustrated in U.S. Pat. No. 4,429,856. A similar valve element having a bellows configuration is disclosed in U.S. Pat. No. 3,385,301. Finally, in U.S. Pat. No. 3,192,949, there is disclosed a valve element having an elongated stem composed of a resilient, porous-form plastic material. Each of these configurations are intended to, on the one hand, assure that the valve seat of the valve element is urged into sealing engagement with the valve seat of the valve housing and, on the other hand, to permit the check valve to be opened (cracked) when sufficient force is exerted on the valve element, either fluidly or mechanically by means of a syringe or the like inserted into the check valve.
It is an object of this invention to provide an improvement which overcomes the aforementioned inadequacies of the prior art devices and provides an improvement which is a significant contribution to the advancement of the check valve art.